1. Field of the Invention
The present invention relates to a three-dimensional image encoding/decoding system, and more particularly to a three-dimensional image encoding/decoding system for encoding/decoding an image signal of an object, a depth signal of the object and an external computer graphic signal.
2. Description of Related Art
Recently, there has been actively made an attempt to compose a real image and a computer graphic image, which is represented by a technique as disclosed by Hayashi, Fukui and Miyata, "Video composing system by integration of real time image processing and computer graphics", in General Meeting of Institute of Electronics, Information and Communication of 1995, D-464 (March 1 1995). However, when this technique is applied to a communication system or an accumulation system, there has not been established any system for naturally composing the real image and the computer graphics while efficiently compressing the real image and the computer graphics.
In "The Virtual Reality Modeling Language", Version 1.1 Draft (December 1995), it is described a description system of computer graphics which is based on applications to a communication system, a memory store system. Specifically, a program description is compressed by using a standard compression system of computer data which is called as "gzip", and then the compressed program description is expanded at an observation side (viewing side) to generate computer graphics. However, this technique never teaches any efficient compression system of a three-dimensional natural image.
A conventional compression system for a three-dimensional natural image typically includes a compression system for compressing one of right and left stereo images, a disparity vector and a disparity compensated prediction error such a compression system has been proposed by W. A. Schupp, Yasuda in "Data Compression of 3-D Moving Pictures using Adaptive Motion/Disparity Compensation", Preview of Picture Coding Symposium of Japan of 1988, 5-1 (1988). However, in this system, a camera parameter is indispensable to numerically determine the depth, and the disparity compensated prediction error is entirely insignificant information if the composition with the computer graphics is considered.
Further, a system for dividing a two-dimensional picture signal into plural hierarchical layers and then performing an image encoding is described by J. Y. A. Wang and E. H. Adelson: "Representing Moving Images with Layers", IEEE Trans.on Image Processing, Vol. 3, No. 5, pp. 625-638 (1994-09). Specifically, an intensity (color brightness) map, a velocity map and an area map are extracted from an input picture signal by an image processing method, and then each of these maps are coded. The intensity map is constructed by information on the color brightness of each pixel. The area map is constructed by information representing an area to which each pixel belongs, an object or transparency. The area map may be constructed by information representing representative positions of a triangular patch, a block or the like. The velocity map is constructed by information representing the motion between adjacent frames of each pixel. The difference from an ordinary image encoding system resides in that an area map representing information of object shape in an image is provided. However, this system has no reference to transmission of depth information.
Various systems such as a passive system and an active system as disclosed by Iguchi and Sato in "3-D shape measurement" issued by Shokodo, pp 11-19 (1990) have been known as methods of measuring the depth. However, these systems take no consideration into a system for adding a natural image with depth information which is obtained by using these systems.
As described above, the conventional three-dimensional image encoding/decoding systems as described above have taken little consideration into the efficient compression of depth information. Therefore, an object of the present invention is to realize a three-dimensional image encoding/decoding systems that performs efficiency information compression and composes depth information, natural computer graphics and the like.